Our earlier application U.S. Ser. No. 936,842 (filed 27 Aug. 1992 and entitled "Variable Hydraulic Machine") includes an extensive "Background" discussion relating to well-known hydraulic pumps and motors, and it discloses several embodiments of fixed- and variable-displacement hydraulic machines which comprise the invention disclosed therein (hereinafter referred to as "our earlier pump/motor invention"). The disclosure of above-identified application Ser. No. 936,842 is pertinent to our invention and, therefore, is fully incorporated herein by reference.
A large percentage of commercially-acceptable hydraulic pump/motors utilize rotating cylinder blocks having reciprocating pistons that ride over an angularly-positioned swash-plate. It has long been known that it is usually more efficient to use fixed cylinders and pistons to cause rotation of a split swash-plate. However, most known designs for mounting of such split swash-plates have proven to be so complex and expensive to manufacture and maintain that split swash-plate designs have not achieved wide commercial acceptance when both relatively high pressures and relatively high speeds are required (e.g., for automotive drives).
Our earlier pump/motor invention, as disclosed in above-identified application Ser. No. 936,842, has cylinders formed circumferentially about the central axis of a cylindrical housing that does not rotate; and connecting rods transfer reciprocal motion between its axial pistons and a nutating swash-plate. The swash-plate is split into a "wobbler" portion, which nutates but does not rotate, and a "rotor" portion, which both nutates and rotates, the rotor portion being connected to a drive element that is aligned with the pump's central axis and supported in a main bearing positioned at one end of the housing. For fixed-displacement embodiments, the rotor portion of the split swash-plate is secured to the drive element at a fixed inclination; while, for variable-displacement embodiments, the inclination of the swash-plate is varied by the movement of its pivot which is attached to a slideable shaft positioned by a servo-mechanism.
Our earlier pump/motor invention is a unique combination of well-known mechanical elements organized and mounted in a novel manner to provide a hydraulic machine capable of operating at improved maximum speeds and pressures while, at the same time, being remarkably reduced in size and weight. Our earlier invention, which is disclosed in several embodiments, comprises an exceptionally compact reciprocating-piston pump unit capable of developing much higher horsepower than known pumps of similar physical dimensions.
While the prior art includes myriad designs incorporating fixed cylinders and split swash-plates, we are unaware of any presently-available commercial hydraulic pumps or motors using such prior art designs for automotive or industrial purposes. Apparently, these prior art designs are either incapable of satisfactory performance under the wide range of pressures and speeds necessary for automotive or industrial operation, or else they are too complex and expensive for commercially-feasible use.
Some part of this apparent lack of success appears to be related to the difficulty of providing an acceptable structure for supporting the split swash-plate so that its wobbler portion is free to follow its complex nutating motion without rotation. It is this latter problem to which the invention herein is primarily directed. In this regard, in another of our earlier applications, namely, U.S. Ser. No. 153,568 (filed 16 Nov. 1993 and entitled "Swash-Plate Mountings for Hydraulic Machines" and now abandoned), we disclosed two different embodiments of swash-plate mounting structures that addressed this problem. That latter application (hereinafter referred to as "our earlier swash-plate mounting invention") also includes a pertinent "Background" discussion relating to this swash-plate mounting problem as well as a bevel-gear mounting assembly for fixed-angle swash-plates and, therefore, it is also fully incorporated herein by reference.
More than fifty years ago, the problems related to providing satisfactory support for the wobbler portion (i.e., the nutating-but-not-rotating portion) of a split swash-plate were thoroughly discussed in U.S. Pat. No. 2,258,127, issued to J. O. Almen in 1941. The key problems relate to supporting a wobbler without unduly affecting its complex motion in which, as it nutates without rotation, every point on its surface follows the pattern of a lemniscate (a figure-eight pattern formed on the surface of a sphere).
The Almen reference discloses a support structure for a fixed-angle swash-plate that it describes as a "uniform velocity universal joint" which is mounted on rolling balls. About a decade ago, this same rolling-ball structure was adapted for a variable-displacement hydraulic machine in U.S. Pat. No. 4,433,596 (issued to J. Scalzo). The structures disclosed in the Almen and Scalzo references are relatively complex and require large numbers of small parts; and the maximum angle to which their swash-plates can be inclined is relatively limited (e.g., to less than 15.degree.). In contrast, with our earlier pump/motor invention and our earlier special mounting arrangements, swash-plate inclinations can be maintained at angles as large as 25.degree.-30.degree. under the high pressure conditions required for industrial use.
For background purposes, reference is also made to known gear mountings for swash-plates used in the non-analogous art of refrigerant gas compressors. We use the term "non-analogous" art because automotive and industrial hydraulic machines run at high speeds (e.g., 2,000 rpm) and high pressure (e.g., 6,000 psi), and persons skilled in the design of such machines do not consider low speed/low pressure refrigerant gas compressors to be part of the same art. Nonetheless, some known refrigerant compressor designs include wobblers supported by a small pair of mating bevel gears aligned by a shared ball that also serves as a bearing between the respective gears. (For instance, see U.S. Pat. No. 3,712,759 issued to Olson, Jr. and U.S. Pat. No. 4,042,309 issued to Hiraga.)
In regard to gear mounting assemblies for split swash-plates, we are aware of only one design that appears appropriate for automotive and industrial use, namely, the bevel gear invention (disclosed in our above-cited earlier swash-plate mounting application) which, in one of our prototype motors, is capable of operating smoothly when the motor is slowed to a full stop and then restarted in either direction while subjected at all times to loads as large as 415 ft. lbs.
Another reason for the lack of commercial success of prior art split swash-plate pumps (for heavy industrial and automotive applications) may relate to the size and weight of the roller-bearing structure required to support the axial thrust of the pistons against the swash-plate assembly. In some commercially-used prior art machines of the rotating cylinder block design, pressure-balanced sliding shoes have been attached to the ends of the rotating pistons to reduce the thrust at the interface between the fixed swash-plate and the pistons. However, such sliding shoes have apparently not been viewed as appropriate for fixed cylinder/split swash-plate machines.